Known methods for forming images used for patterning of semiconductor integrated circuits, liquid crystal display elements and printed circuit boards include methods that utilize positive photoresists comprising combinations of novolac-type phenol resins and 1,2-quinonediazide compounds.
Such a positive photoresist is alkali-insoluble at the unexposed sections and alkali-soluble at the exposed sections, so that the resist at the exposed sections is removed during alkali development. The 1,2-quinonediazide compound interacts with the novolac-type phenol resin at the unexposed sections during that time, acting as a dissolution preventer to render them alkali-insoluble. At the exposed sections, the 1,2-quinonediazide compound dissolves under the ultraviolet irradiation, undergoing Wolff rearrangement to produce an indene ketene. The indene ketene in addition reacts with water to produce an indenecarboxylic acid. This indenecarboxylic acid is acidic, while the residual novolac-type phenol resin is also weakly acidic because of its phenolic hydroxyl groups. The exposed sections are therefore rendered soluble in the strong alkaline aqueous solution of tetramethylammonium hydroxide.
However, development with strong alkaline aqueous solutions such as tetramethylammonium hydroxide can sometimes lead to peeling of the unexposed sections as well. When this occurs, the positive photoresist fails to exhibit adequate resolution. The use of strong alkaline aqueous solutions is also problematic from the viewpoint of safety and waste water treatment, as well as other environmental issues.
A demand therefore exists for a photosensitive resin composition that can be sufficiently developed even with weak alkaline aqueous solutions.
It has been attempted to meet this demand by enhancing the properties of photosensitive resin compositions. For example, there have been proposed photosensitive resin compositions containing compounds obtained by addition of acid anhydrides to reaction products of novolac-type epoxy compounds and unsaturated monobasic acids (see Patent documents 1-5). There have also been disclosed thermosetting/photocuring compositions containing a carboxyl group-containing, obtained by reacting an unsaturated monobasic acid with the reaction product of a novolac-type phenol resin and an alkylene oxide and reacting an acid anhydride with the resulting reaction product (see Patent document 6). Also proposed have been positive photosensitive resin compositions employing novolac-type phenol resins obtained by reaction between an acid anhydride and the alcoholic hydroxyl group of an alcoholic hydroxy group-containing novolac-type phenol resin (see Patent document 7).    [Patent document 1] Japanese Unexamined Patent Publication SHO No. 61-243869    [Patent document 2] Japanese Unexamined Patent Publication HEI No. 3-253093    [Patent document 3] Japanese Unexamined Patent Publication HEI No. 6-192387    [Patent document 4] Japanese Unexamined Patent Publication HEI No. 7-41716    [Patent document 5] Japanese Unexamined Patent Publication HEI No. 9-136942    [Patent document 6] International Patent Publication No. WO02/024774    [Patent document 7] Japanese Unexamined Patent Publication No. 2001-114853